In the comic strip Blondie, Dagwood constantly eats comically large sandwiches. He's so well known for it that his name has entered the dictionary meaning "a thick sandwich filled with a variety of meats, cheeses, dressings, and condiments", and he's the Trope Namer for that type of sandwich. It's also a popular name for sandwich shops in the midwest. In Belgium, Dagobert (the French name for Dagwood) is the name of (thick) sandwiches made from a half French bread filled with lots of ham, cheese, salad, tomatoes, carrots, mayonnaise and sometimes onions.
Peter and Roger from FoxTrot; while Peter does this year-round (even eating groceries before his mother has gotten them to the parking lot of the store), he and his father really shine on Thanksgiving. This is often exaggerated as he's shown to be very heavy despite the similar body shape.
The title character of Curtis not only has a bottomless stomach, but one made of cast iron, capable of eating quantities and combinations of food that sicken his parents just thinking about it.
Garfield-To the point that a few times, his legs couldn't even reach the ground. It's pointed out he only stops eating when there's nothing left in the house.
Billy Bunter, a British character who first appeared in prose (in the Greyfriars stories) in 1908 and made the transition to comics in 1940.
Sarge and Louise Lugg from Beetle Bailey. He's usually specifically excluded from local "all you can eat" offers, and together they need a table for four at a restaurant, as well as being fond of other variations of I'll Take Two Beers Too.
He's more muscular than "fat", but Ox from Luann has a platinum credit card given to him by his parents to buy his lunches, which tend to be large. He once ordered every item on the menu of Wienie World using it.